Gasoline-fueled motor vehicles have many sites from which hydrocarbons (HC) may evaporate into the environment, thereby contributing to the formation of smog. One such known site is the intake manifold of a carbureted or port-injected internal combustion engine. As HC emission regulations are tightened, a means is needed to prevent residual HC vapor from escaping from the intake manifold through the throttle valve assembly after engine shutdown. Known approaches have included, among others, closing off the intake and idle air with the throttle valve when the engine is shut off; adding adsorptive carbon grids in the intake air flow path between the air cleaner and the engine throttle plate; and lining the intake manifold, other air ducts, and/or the air cleaner with adsorptive carbon sheeting.
Employing an engine's electronic throttle control to close the intake at shut down may impair the desirable option of a so-called “limp home” mode in which a vehicle may be driven in event of a partial failure of the engine electronics control system. Systems with mechanical throttles not employing electronic throttle control typically do close the throttle at shut down, leaving a separate “idle air” passage open. In these systems, achieving a completely sealed manifold is difficult and expensive.
Adsorptive grids in the intake air flow path are undesirable as they are expensive to fabricate, brittle and therefore vulnerable to breakage, and inherently restrict the volume of intake air.
Carbon sheeting applied to inner surfaces of the manifold and air ducts is only partially successful because much HC laden air can escape the manifold without being brought into proximity with an adsorptive surface. Relatively large areas of carbon sheeting are required to ensure that an adequate quantity of HC comes into contact with the adsorber.
What is needed in the art is a means for increasing the efficiency of hydrocarbon adsorption during engine shutdown at the main air entrance to an engine.
It is a principal object of the present invention to reduce hydrocarbon emissions from a shut down internal combustion engine.